Decorative concrete with uniform surface and method of forming the same

ABSTRACT

A decorative concrete with a very uniform finish surface and a method of fabricating the same is disclosed. A concrete mixture is poured over a subgrade which defines an exposed surface. The exposed surface is finished with any of several techniques, and the surface is then worked with an abrasive material, and additional techniques are used to color and seal the concrete.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable

BACKGROUND Field of the Invention

The present invention relates in general to concrete products, and moreparticularly, to a method of creating decorative concrete with a highlyuniform surface and the method of forming the same.

Description of the Related Art

As is well known in the building and construction trade, concrete isextensively utilized as a building material for commercial andresidential applications. In this regard, due to its durability, waterresistance, and cost economy, concrete has gained widespread use. Withthis widespread use, there is a demand for decorative concrete thatpossesses improved aesthetics such as a highly uniform surface.

Although numerous methods of concrete finishing have been developed inprior art, such as salt finish, broom finish, and form pressed finish(i.e. stamp concrete), the use of such conventional techniques havetypically failed to provide the desired result, i.e. aesthetics, of theresultant concrete surface to be highly uniform. In this regard,although techniques have been developed to provide a more uniformconcrete, such attempts have been generally difficult or costly toinstall. Further, such prior art methods have typically focused onworking the concrete before hardening by surface treating the concretewith additional material while the concrete is still in a plastic state.

As such, there exists a need in the art for decorative concrete with ahighly uniform finish, as well as an economical method of forming thesame. Various aspects of the present invention are specifically directedtoward addressing these particular needs as will be discussed in moredetail below.

BRIEF SUMMARY

The present invention is best understood by reference to the followingdetailed description when read in conjunction with the accompanyingdrawings.

Disclosed is a method of forming a decorative concrete surface having ahighly uniform exposed surface, preferably including preparing asubgrade, pouring a concrete mixture over the subgrade, the concretemixture defining the exposed surface when poured, applying a finishtechnique to the exposed surface, working the exposed surface with anabrasive compound and applying a surface retarder to the exposedsurface.

The method further may include the steps of washing the surface film,curing the concrete with water, and power washing the top surface. Themethod can further include sand blasting; acid washing; and/or applyingaggregate to the top surface of the concrete.

After the concrete has hardened, the method utilizes an abrasive, suchas a low grit sandpaper, which is applied to the top surface of theconcrete. Preferably the sandpaper comprises a twenty grit sanding discwhich may be mechanically or manually run over the top surface of theconcrete. Although intuitively the application of a low grit sandpaperon the top surface of the concrete would seem to make the top surface ofthe concrete uneven and/or rough, the applicant has found that itactually evens out the sand particles creating a more uniform finish onthe top surface of the concrete.

Following the abrasive sanding application, the top surface of theconcrete may optionally be provided with conventional surface treatment,such as concrete stain and/or concrete sealers as desired. The method ofthe present invention can be utilized for both new concreteinstallations and is suitable for use on nearly all concrete finishingtechniques, such as brooming finish, hand trowel finish, sand blastfinish, stamp concrete finish, or acid wash finishes. Further, thepresent invention is additionally suitable for use on existing concreteinstallations as a retrofit application to improve the uniformity andaesthetics of the top surface of existing concrete installations.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the various embodimentsdisclosed herein will be better understood with respect to the followingdescription and drawings, in which like numbers refer to like partsthroughout, and in which:

FIG. 1 illustrates a perspective cross sectional view of the decorativeconcrete structure of the present disclosure;

FIG. 2 illustrates the method of forming the decorative concrete; and

FIG. 3 illustrates the step of working the concrete with an abrasivematerial.

DETAILED DESCRIPTION

Referring first to FIGS. 1 and 2, the decorative concrete structure 10of the present invention providing a highly uniform surface and themethod for preparing a decorative concrete structure 10 is shown.Various aspects of preparing the decorative concrete structure 10 resultin a decorative concrete structure 10 which provides a highly uniformsurface of the concrete.

An initial step in forming the decorative concrete structure 10 mayoptionally comprise preparing a subgrade 8. The subgrade 8 may provideuniform support for the decorative concrete structure 10. Typically, theinitial step involves excavating the ground to a desired elevation andcompacting the ground preferably to 90% compaction to ensure a uniformand stable support. After compacting the subgrade 8, the subgrade may becovered with a layer of clean, moist, fill sand 12 which preferablydefines a minimum thickness of approximately four inches. Although thefill sand 12 is not necessary for the method of producing the decorativeconcrete structure 10, it is desirable to control the hydration processof the decorative concrete structure 10.

After preparing the subgrade 8, should such a preparation be required oroptionally chosen, conventional forms or form members may be placedaround the perimeter of the designated pour area 15 to create a cavitywithin which the concrete mixture 16 is poured. As is well known, theform members create a solid barrier that maintains the concrete mixture16 in place and forces the concrete mixture 16 to assume a desiredexternal boundary configuration. The form members may be fabricated fromplywood, plastic, aluminum, steel, or other materials known in the art.

Optionally, and depending on the requirements of the work site or theuse of the concrete at the site, after preparing the forms for thedecorative concrete structure 10, reinforcing members 14 such as rebaror a wire mesh may be used to increase the resultant strength of thedecorative concrete structure 10. The reinforcing members 14 provideincreased strength and/or mitigate the likelihood of cracking within thedecorative concrete structure 10. The reinforcement members 14 may bepositioned upon conventional concrete chairs disposed over the layer offill sand 12 to define a lattice framework, or other arrangements knownby those skilled in the art.

After the reinforcing members 14 are placed, should the reinforcingmembers be required or optionally chosen, a conventional concretemixture 16 is poured within the forms. The concrete mixture 16 ispreferably poured to define a depth of approximately 3.5-4.0 inches,however, other depths are also contemplated. Although variations in theconcrete mixture 16 are contemplated, the preferred concrete mixture 16comprises 70% sand and 30% aggregate combined with portland cementpreferably (2,000 pounds per square inch) or (3,000 pounds per squareinch). Further, depending on desired aesthetics of the exposed surface18, an integral color additive may be added to the concrete mixture 16to achieve the desired state.

After the concrete mixture 16 has been poured, the top surface of theconcrete mixture 16 is screeded to produce a flat surface that definesthe exposed top surface 18. The top surface 18 of the concrete mixture16 is screeded to remove excess concrete and to bring the top surface ofthe concrete mixture 16 to a desired plane or grade determined by theform members.

After screeding the concrete mixture 16 to the desired plane or grade,the exposed surface 18 may be surface finished with a conventionalfinishing tool to dispose a quantity of the cement/fine paste derivedfrom the concrete mixture 16 at the exposed surface 18 thereof. Forexample, a float tool such as a bull float 17 or vibrating bull floatmay be used to create a smooth and flat upper surface and to removesurface imperfections. In addition to bringing up the appropriate amountof cement/fine paste, the float may seal the exposed surface 18 of theconcrete mixture 16. An exemplary metal bull float is sold under thetrademark HAL200 by the Lievers Holland Co. although other floats arecontemplated herein.

After finishing with the float tool 17, a conventional trowel tool maybe applied to the exposed surface 18. The troweling may be accomplishedby a mechanical trowel machine or manually by a hand trowel.

In an optional step, while the exposed surface 18 of the concretemixture 16 is still in a plastic state, fine sand or aggregate, or acombination thereof 22 may be broadcast over the exposed surface. Thefine sand, aggregate, or combination thereof 22, may be of any givencolor or texture, as required to produce the desired finish appearance24. Further, it is contemplated that various combinations of color,texture, or other characteristics of the fine sand may be variouslycreated in order to accurately simulate, for example, quarried stone.Examples of such methods are known in the art and are disclosed, forexample, in U.S. Pat. Nos. 8,079,775 7,781,019, 7,614,820, and 5,794,401to Shaw et al., the contents of which are expressly incorporated hereinby reference.

It is further contemplated that the exposed surface may be worked firstwith a conventional brooming tool 24 to create patterns in the exposedsurface that resemble wood grain.

According to an implementation of the present invention, it iscontemplated that the broadcasting of the fine sand and the aggregatemay be performed utilizing pneumatic equipment. The pneumatic equipmentmay allow the operator to produce a randomized pattern or a designcorresponding to a particular natural material. Thus, the appearance ofthe exposed surface may be enhanced utilizing other tools such aspneumatic equipment.

After being broadcast upon the exposed surface of the concrete mixture,the fine sand and the aggregate are mixed or worked 23 into the exposedsurface 18 of the concrete mixture 16, and more particularly are mixedinto the cement/fine paste of the exposed surface. This may beaccomplished utilizing a power trowel. However, it is contemplated thatthe mixing may be accomplished utilizing other devices known in the art.

Once the exposed top surface has been finished with any of the foregoingmethods, the concrete mixture is allowed to harden 25 which typicallyoccurs within twenty-four to forty-eight hours after the concrete ispoured.

In an optional step, after the concrete has hardened, the exposedsurface may be acid washed or sandblasted 35 to expose the aggregateswithin the concrete. Essentially, the sand blasting erodes the surfacelayer of the concrete, but sand blasting can do more depending on thechosen grade of sand blasting.

After hardening of the concrete mixture 16, and optional application ofone or none of the above finish techniques, the exposed top surface 18is treated by applying an abrasive or abrasive member in a side-to-sidesweeping reciprocal or in a rotary motion. The side-to-side sweepingreciprocal motion is indicated by the arrows on either side of themachine 100 in FIG. 3. The abrasive may be sandpaper, emery cloths orhoning stones, or similar abrasive discs or pads 40 to achieve thedesired uniform finish appearance 24. The abrasive may have any one ofvarying degrees of abrasiveness in order to treat the exposed surfaceand achieve the desired finish appearance 24. For example, depending onthe techniques used on the concrete used prior to and during hardening,a more or less abrasive material may be required to achieve the desiredfinish appearance 24. A range of abrasiveness exemplified by 10 grit to4000 grit sandpaper is contemplated. For most applications, 20 gritsandpaper is used, but other grades of sandpaper as well as otherabrasives are contemplated depending upon the surface finish applied inthe previous step and the desired end finish.

As shown in FIG. 3, the sandpaper may be worked across the exposedsurface either by hand or machine 100. Conventional machines that may beused in working the exposed surface may include a rotary polisher, orrotary sander, a belt sander or a reciprocating sander. Any of theabrasives may alternatively be worked by hand, including the use of handtools, for example, a sanding block, or handheld power tools, such as ahandheld reciprocating sander or handheld belt sander.

Typically, the machines will be used with sandpaper manufactured forattachment to the machine. The sandpaper may be in either in disk, beltor sheet formats, as required by the configuration of the machine. Theabrasive particles embedded in the sandpaper act to either remove orfracture small sand particles in the exposed surface 18, which createsthe more uniform final finish for the exposed surface, giving it thedesired finish appearance 24. However, either purpose manufactureddisks, belts, or sheets of alternate materials, or custom manufacturedcombinations of materials and formats may be used as well. For example,a user may manufacture a belt emery cloth for use in a belt sander.

Further, a process of working the exposed surface with progressiveabrasives is contemplated. Again, depending on the techniques used whilethe concrete is still plastic, more or fewer steps may be required. Forexample, in a first step, the exposed surface may be worked with 10 gritsandpaper, in a next step, the exposed surface is worked with a finergrit sandpaper, for example, 80 grit. In a final step, the exposedsurface is worked with an even finer grit sandpaper, for example, 100grit. In using this method, the particles removed or fractured in eachstep become increasingly smaller, and the exposed surface takes on amore and more uniform appearance. Depending on the starting point of theexposed surface due to the various techniques used while the concretewas still plastic, only one or two steps, instead of three, may berequired.

The preferred embodiment for large, essentially flat areas of exposedsurface uses a rotary polisher or rotary sander and a disk 102 ofsandpaper, but, as noted above, other machines and shapes of abrasivemay be used, including belt and reciprocating sanders, with belts,squares or rectangles of sandpaper or other abrasives. The use of therotary polisher or rotary sander, especially where the sandpaper isapplied either in a generally rotary or side-to-side sweeping reciprocalmotion, lends to the easiest achievement of a uniform surface.

Some circumstances may render the use of a rotary machine eitherimpossible or impractical. In such circumstances, the desired highlyuniform appearance may be best achieved by the use of alternativemachines or working the surface by hand. For example, conventional beltor reciprocal sanders may be used on the treads of a concrete stairway.In such circumstances, the best motion to work the exposed surface maybe a one-way or back-and-forth linear reciprocating motion. The verticalsurfaces of the risers of the stairway may be best worked by hand, or byhandheld power tools. Working the exposed surface by hand or withhandheld tools allows for a wide range of techniques, as the overallmotions tend to be smaller, and are more easily controlled. Thus, anytime the exposed surface is worked by hand, as in the case of therisers, the circular or reciprocating sweeping motions of the rotarypolisher or rotary sander, or the more linear techniques discussed inconjunction with the belt or reciprocating sander may be used.

In an alternative method, large flat areas may be worked by machine, andthen areas determined by the user to require additional working may bedone by either machine or hand. For example, it is known by one ofordinary skill in the art that when using a rotary polisher or rotarysander, linear boarders, such as edges where the concrete ends, andlandscaping begins, or where the exposed surface abuts a structure, aredifficult to work uniformly. After using one machine, such as a rotarypolisher or rotary sander in such an area, anther machine, for example,a belt sander may be used to work any exposed surface requiringadditional working to achieve a highly uniform finish. Alternatively,such areas may be worked by hand to ensure that crossover, and thecorresponding possibility of overworking certain areas relative toimmediately adjacent areas, is minimized.

As another alternative, different techniques may be applied in adjacentareas to create a pattern. For example, where there may be conventionalsaw cuts made in the surface of the concrete in order to controlcracking. One area defined within certain saw cut borders may be treatedto a finish appearance using a chosen grade of abrasive, while anadjacent area, defined by at least one common saw cut, is finished to adifferent finish appearance using a rougher or finer grade of abrasive.

Again with reference to FIGS. 1 and 2, following sanding the exposedsurface 18, an optional concrete stain 45 or sealer or protective coat50 may be applied to achieve a final desired appearance 24 and texture.

As illustrated in FIG. 2, the concrete mixture may be cured utilizingwater alone 70, as opposed to chemical curing agents in order to avoidstaining of the exposed surface. Such water curing may typically befacilitated through the use of a conventional fogger or soaker hose.After a prescribed period of time (e.g., 30 days after initiating thecuring process) any surface residue present on the exposed surface isremoved by conventional power washing 75 with a ninety percent (90%)steam and ten percent (10%) muriatic acid mixture which is applied by apower washer via a high pressure nozzle.

The above description is given by way of example, and not limitation.Given the above disclosure, one skilled in the art could devisevariations that are within the scope and spirit of the inventiondisclosed herein, including various ways of cutting into the exposedsurface 12 to create a pattern that resembles planks found inconventional natural wood decks. Further, the various features of theembodiments disclosed herein can be used alone, or in varyingcombinations with each other and are not intended to be limited to thespecific combination described herein. Thus, the scope of the claims isnot to be limited by the illustrated embodiments.

What is claimed is:
 1. A method of forming a decorative concrete slabhaving a highly uniform exposed surface, comprising: pouring a concretemixture over the subgrade, the concrete mixture defining an exposed topsurface when poured; finishing the exposed top surface; allowing theconcrete to harden; and working the exposed top surface with anabrasive.
 2. The method of claim 1, further comprising the steps ofwashing the surface film, curing the slab with water, and power washingthe slab.
 3. The method of claim 1, further comprising sand blastingafter allowing the concrete to harden.
 4. The method of claim 1, furthercomprising acid washing after allowing the concrete to harden.
 5. Themethod of claim 1, wherein finishing the exposed surface comprisesapplying aggregate.
 6. The method of claim 1, wherein the abrasive issandpaper.
 7. The method of claim 1, wherein working the exposed surfacewith an abrasive is done with a machine.
 8. The method of claim 1,wherein working the exposed surface with an abrasive is done by hand. 9.The method of claim 1, wherein finishing the exposed surface comprisesapplying fine sand.
 10. The method of claim 1, further comprising thestep of placing reinforcement members above the subgrade and pouring theconcrete mixture over reinforcement members so that the reinforcementmembers are encapsulated within the concrete mixture.
 11. The method ofclaim 10, wherein the reinforcement members are rebar or a wire mesh.12. The method of claim 1, wherein finishing the exposed surfacecomprises applying a mixture of fine sand and aggregate.
 13. The methodof claim 1 further comprising the step of applying a stain after workingthe exposed concrete surface with an abrasive.
 14. The method of claim 1further comprising the steps of: preparing a concrete form for thedecorative concrete slab, the concrete form defining a boundary of thedecorative concrete slab; and applying a surface retarder after workingthe exposed surface with an abrasive.
 15. The method of claim 14 furthercomprising forming a vapor barrier after applying the surface retarder.